Permanent magnet couplers of the general type disclosed in U.S. Pat. No. 5,477,094 have a magnet rotor and conductor rotor interacting to transmit power between input and output shafts. The magnet rotor has a plurality of circumferentially spaced permanent magnets having their opposite poles separated by air gaps from electro-conductive conductor elements provided by the conductor rotor on opposite axial sides of the magnet rotor. For many applications it is preferred that the air gaps be readily adjustable after installation of the coupler to obtain or vary "soft start" at start up, meaning that initially during start up there is a noticeable rotational slip between the rotors which gradually reduces to a minimum in a few seconds as the output shaft builds up speed from zero to a maximum. Less starting torque is required to drive a given load if the coupler is matched to the load such that there is a soft start experienced during start up. Also, there is less shock to the power transfer system when soft start is provided.
Providing for adjustment of the air gaps permits a given magnetic coupler to be suitable for maximum performance in a variety of load applications without a need to change the number of magnets in the magnet rotor. Providing for such adjustment after installation of the coupler makes it possible to field adjust soft start of a coupler without removing or disconnecting the coupler if the load at the installation is changed.